1. Field of the Invention
This invention relates, in general, to electrical apparatus and, more specifically, to arrangements for banding together groups of conductors in the end windings of turbine generators.
2. Description of the Prior Art
Electrical conductors which form the coils of electrical apparatus windings must be sufficiently secured to prevent movement of the conductors and damage to the insulation therearound. In large rotating electromechanical apparatus, the large mechanical forces to which the conductors are subjected makes it a difficult task to properly secure the conductors. The conductors of the stator end windings in large turbine generators are typical of conductors where difficulty has been experienced in the prior art in satisfactorily and economically securing the conductors. Ideally, the conductor securing arrangement should firmly secure the conductor throughout the life of the machine and should offer convenient and effective repair techniques if alteration or replacement of a conductor is necessary.
The end winding conductors of turbine generators have been secured by several different arrangements according to the prior art. One arrangement involves the tying together of adjacent conductors by wrapping a glass roping around the two conductors. This wrapping or tie arrangement is repeated throughout the entire winding, thus every conductor is tied directly to an adjacent conductor at least at one position along the conductor. Typically, the two-conductor ties are staggered throughout the end turns of the winding to provide several ties to each conductor. As with other prior art arrangements and the new arrangement disclosed herein, suitable spacers are usually positioned between the conductors and are held in place mainly by the force between the conductors created by the wrapping arrangement.
While the wrapping of adjacent conductors pairs with glass roping has been satisfactory for smaller apparatus, such an arrangement is not completely desirable for large apparatus wherein the conductors are subjected to relatively large forces. Due to the multiplicity of ties, the securing of conductors according to this prior art arrangement is very laborious and time consuming. In addition, the amount of force which holds the conductors together is dependent upon the tension in the tie, which is highly dependent upon the ability and consistency of the person making tie. With such an arrangement, it is difficult to assure that all of the ties will have enough tension to properly restrain the conductors. Also, since the roping is wound around the conductors several times, there is not any convenient way to re-tighten the ties should it later be desirable to do so.
Another useful prior art arrangement for securing the end winding conductors of turbine generators is disclosed in U.S. Pat. No. 3,135,888. According to that patent, a two-piece strap assembly consisting of cured-in-place glass fiber roving is used to secure several conductors together. In the completed apparatus, the lower portion of the strap assembly is rigid and conforms to the shape in which it was cured. Due to the rigid characteristics of the lower portion of this prior art strap arrangement, certain properties of the complete strap assembly are inherent. Since the desired tension is put into the lower strap before it was cured into a rigid structure, it is not feasible to re-tension the rigid strap which extends around the corners of the conductors without putting undesirable stresses in the cured material and in the strap where it blends around the corners of the conductors. With this restriction, such strap assemblies are not very suitable for conductor replacement or re-tightening any time after final assembly. Therefore, it is also desirable, and it is another object of this invention, to provide an arrangement for connecting together end winding conductors which is suitably constructed for conductor replacement and re-tensioning after the apparatus has been in operation.
End winding conductors are separated by suitable spacer blocks which are placed in compression by the strap assembly around the conductors. Due to the constant compressive forces, the minute mechanical movements of the conductors, the operating temperature of the apparatus, and other factors, some of the spacer blocks have been known to become loose after a period of operation. Although an initial tensile force is developed in the rigid strap assembly of the prior art, the compressive forces on the spacer blocks are quickly reduced if they become slightly smaller, since the elongation of the rigid belt is small. Thus, with a rigid strap constructed according to the prior art, small decreases in spacer size produce relatively large decreases in the compressive force holding the conductors and spacer blocks together. Therefore, it is desirable, and it is another object of this invention, to provide a conductor restraining arrangement wherein the force holding the conductors and spacer blocks together is not changed appreciably when the spacer blocks decrease in size during the life of the apparatus.
The requirement that the lower strap be cured after it has been placed in the apparatus and tensioned presents some inconvenient construction steps. Since the lower strap is substantially non-exposed, local heating of the strap to produce curing is a difficult procedure. Heating of the complete apparatus is also relatively difficult when the size of such machines is taken into consideration. The use of a material which cures at room temperature eliminates the heating inconveniences, but the shelf life of the material is short and the application thereof would have to adhere to a definite time schedule. Therefore, it is also desirable, and it is still another object of this invention, to provide an arrangement for connecting together end winding conductors which does not require that the lower strap or belt be cured after it has been placed into the apparatus.